Polymers of Benzidine were synthesized by hydrogen peroxide reaction catalyzed by horseradish peroxidase enzyme. The polymerization reaction was carried out at room temperature in a monophasic organic solvent with a small amount of water at pH 7.5.

The technique of degenerate four-wave mixing (DFWM) with nanosecond and picosecond pulses was employed to measure the third-order nonlinear optical susceptibility χ. The samples were studied in solution in Dimethyl sulfoxide:Methanol in volume ratio 4:1. The observed values are of order 10−9 to 10−8esu. Measurements on a thin film agree approximately with the extrapolated values fron solution measurements. Picosecond time resolved measurements indicate a pulse-width limited response followed by a small slow component. Investigation of the total energy transmission as a function of the incident intensity and fluence at 532 nm for pico- and nanosecond pulses indicates reverse saturable absorption. As we observe the nanosecond and picosecond curves to be superimposed for the intensity plot but not for fluence, we conclude that the nonlinearity is predominantly due to two-photon absorption. Numerical analysis of the data yields a value of 12.25 cm/GW for the two-photon absorption coefficient β. The imaginary component of χ obtained is 5 × 10−9esu. The material appears to be a good candidate for applications in optical power limiting and switching.

This paper describes the development of high quality solid state optical components which have been made by the incorporation of the reverse saturable dye chloro aluminium phthalocyanine (CAP) into polymeric host material.

In particular, the effect of using different host materials with CAP is investigated in terms of key parameters such as solubility, integrity of the dye molecules in the polymer host, hardness of the resulting polymer, ease of polishing to the production of a good optical finish, induced stress, and non-linear absorption performance.

Results are presented highlighting the above considerations, and problems encountered in material preparation will be described together with details on how, by careful choice of guest/host combination, good optical quality samples can be produced.

Systematic studies of the nonlinear optical properties of metallo-organic materials have led to the development of promising new phthalocyanine materials for optical limiting. Several heavy metal substituted phthalocyanines exhibit a strong nonlinear absorption that is useful for optical limiters in the visible. In fast optical systems, other mechanisms, such as the thermal refraction, contribute to the limiting. The spectral window for limiting can by modified by altering the molecular structure.

The two-photon absorption cross-section for diphenylbutadiene heated to the isotropic liquid state has been measured using the Z-scan technique. In this experiment, the solid diphenylbutadiene was heated using a temperature controlled hot stage above its melting point. Z-scan measurements using 35ps laser pulses at 532nm were then carried out on molten diphenylbutadiene. The value of the two-photon absorption cross-section at 532nm was measured to be σ2 = (38±8) × 10−50cm4s/photon-molecule. This value corresponds well with the cross-section measured previously for diphenylbutadiene dissolved in chloroform using the degenerate four-wave mixing technique.

Using the combination of experimental (DFWM) measurements and electronic structure calculations, ligand electron donating power and explicit solvent interactions were shown to have critical roles in enhancing the χ3 yields for phosphonitrilic materials. Experimental measurements have shown that decreasing solution pH to 1.0 can significantly increase the χ3 yield for P3N3(NHCH3)6 and P3N3(N(CH3)2)6. Corresponding electronic structure calculations indicate replacement of amino by thiomethyl groups will also significantly enhance these yields. Comparison of electrostatic-based solvation effects and explicit water molecules indicates that dielectric stabilization from the solvent plays a minor influence on χ3 in comparison to strategies which affect the strong P-N bond polarity.

A ∼13% increase in the absorption coefficient is seen by a weak probe beam to build-up exponentially in ∼50 ps and decay in ∼1.4 ns after a ∼30 ps intense pump pulse (∼220 mJ/cm2 ) at 532 nm goes through a bis-benzothiazole/H2SO4 solution. We propose a three-level model to explain the effect and obtain the basic parameters by fitting our data to the model.

Optical limiting in toluene solutions of substituted benzanthracene- 3,4 diones and three other quinones, namely, benzpyrene-7,8-dione, benzphenanthrene-3,4-dione and chrysene-5,6-dione was investigated at laser wavelengths 532 nm and 694 nm. Low limiting threshold values of the order of 0.01J/cm2 were obtained for some of the quinones at 532nm. Strong triplet-triplet absorption at the excitation laser wavelengths may explain the optical limiting behavior.

The non-linear optical properties of chloro-aluminium phthalocyanine and 1,3,3,1′,3′,3′- hexamethylindotricarbocyanine have been studied as model systems using z-scan and time resolved experimental techniques. Excited state lifetimes and absorption cross sections have been measured as well as the spectral response of the induced absorption. Excited state lifetimes are critical in determining the performance of a reverse saturable absorber. Even though a first excited state absorption cross section may be large compared with the ground state absorption cross section the lifetimes and transition probabilities of higher lying states can lead to constraints upon how effective organic dyes are as optical limiting materials.

Both novel saturation of the induced absorption at high laser fluences and intermolecular quantum beats in 1,3,3, 1′,3′,3′-hexamethylindotricarbocyanine are demonstrated experimentally and accounted for theoretically. Quantum chemical calculations have been developed to propose a probable inter-molecular mechanism for the observed quantum beats.

Recent progress on the use of molecular engineering approaches for the enhancement and spectral tuning of the optical limiting responses of phthalocyanine complexes is presented. Examples are given involving the use of the heavy-atom approach to enhance the limiting response of naphthalocyanines and of donor substitution of naphthalocyanines to red shift the optical limiting response, as demonstrated for indium and tin octabutoxynaphthalocyanines. These approaches have led to new materials for optical limiting with potential for high performance. An experimental demonstration of the “bottleneck” limiter concept, in which the optical-limiting material is distributed nonhomogeneously to permit strong pumping of excited-state population throughout the interaction region, is presented and shows an order-of-magnitude increase in pulse suppression compared to a homogeneous distribution, without an increase in linear absorbance.

Optical limiting in a solution of tetrabenzporphyrin (TBP) dissolved in tetrahydrofuran (THF) was measured in an f/5 optical focusing arrangement using 532 nm wavelength laser light with a 9 ns pulse duration. The performance of this solution was compared to a variety of other materials. In order to better understand the nonlinear behavior of this material, apertured and unapertured Z-scans were performed. From these measurements it was determined that the excited-state cross section and its ratio to ground-state cross section were large. The nonlinear refraction of this material is made up of contributions from thermal density change and population redistribution. Limiter performance was modeled in an f/64 limiter. The limiter behavior of a slightly modified compound and an additional solvent were measured.

To explore the use of phthalocyanine materials as a solid-state component in an optical limiter, the issues of morphology, film processing and optical limiter activity/stability are investigated. Metal-free and lead phthalocyanine films with glassy morphologies are obtained by chemically functionalizing the ring periphery with an amine-epoxy substitution. Uniform films were obtained by a shearing technique. Comparative optical measurements are made on the amine-epoxy lead phthalocyanine compound as a concentrated solution and as a glassy thin film. Both the solution and film are reverse saturable absorbers at 590 nm. The concentrated solution is a very effective optical limiter. The glassy thin film is susceptible to damage (cavitation caused by the incident beam) and performs comparably only at low incident energies. A liquid matrix may have the benefit of self-healing such damage.

Aluminophthalocyanine and fullerene were trapped in solid transparent matrices using the sol-gel process. The covalent bonding to the matrix improved the chemical stability of the fullerene doped sample. Solid state optical limiting at 532 nm, mainly due to reverse saturable absorption processes, was observed with such samples. The non-linear transmission threshold was typically about 10 mJ/cm2 and an induced density of 1.6 was observed with three orders of magnitude greater illumination. Fluorescent decay measurements support the choice of a three energy level absorption model for the process, which allows indirect measurement of the excited-state absorption.

Nonlinear optical properties of transition metal-phosphine complexes have been measured at 532 nm by degenerate four-wave mixing. Large second-order molecular hyperpolarizabilities, γ, have been found for complexes containing two phosphine ligands. The measured γ values are closely related to the type and coordination geometry of the phosphine ligands, and the γ values vary as the fifth power of the number of substituents with π-electrons structure.

A survey study of solvent effects on the linear and nonlinear absorption properties of C60 has been done. The nonlinear absorption measurements are done at 694 nm with a Q-switched Nd:YAG pumped dye laser. In conjunction with this study a three level rate equation system has been solved analytically and the model results used to extract effective excited state cross sections. A difference and a ratio are calculated from the effective excited state cross section and the ground state cross section. The analysis demonstrates that it is this difference and the initial transmission which determine the critical fluence for the onset of nonlinear absorption. The saturation behavior is determined by the ratio of the cross sections and the initial transmission. Based on these findings C60 is shown to have some of the highest reported nonlinear absorption properties at 694 nm. The effective excited state cross sections at 694 nm are reported for the solutions and correlations to the solvent types demonstrated.

Complex formations in C60 solutions have previously been observed in diethylaniline. In a wide survey of solvents conducted in our laboratory, several additional solvents exhibited complexing behavior with C60 when analyzed with UV-Vis and fluorescence spectroscopy. All solvents with complexing behavior contained nitrogen. They are benzonitrile, N-methylpyrrolidone, and triphenylamine. A careful study was done to characterize the formation of the complexes formed in C60/toluene solutions when each complexing agent was added. Diethylaniline was added to the study as a reference complexing system. Formation of the complexes was followed with UV-Vis and fluorescense spectroscopy. Nash plots of the complexes were done to determine the equilibrium constant and the isosbestic point for each system. Nonlinear optical characterization of the complexing solvents was analyzed.

The development of optical technologies requires the fabrication of reliable optical switching and limiting devices. Optical switches modulate the transmission or reflection of incident light, while optical limiters serve to limit transmission to prevent the transmitted light intensity from exceeding a defined level. A major application of optical limiters is to protect delicate sensors.

Mixed metal clusters (n-Bu4N)2[MoCu3OS3X3] (X = SCN, Cl and Br) were synthesized by solid state reactions. X-ray single crystal diffraction data show that the anionic clusters assume nest shaped structures. The clusters exhibit large self-defocusing effect as demonstrated by their Z-scan traces. The effective third-order polarizability of |γ| = 4.8 × 10−29 esu was determined for (n-Bu4N)2[MoCu3OS3(SCN)3] by a degenerate four-wave mixing technique with 7-ns laser pulses of 532 nm wavelength. An irradiance-dependent transmission measurement was conducted to assess the contribution of nonlinear absorption to the γ-value. These results in combination with the self-defocusing property of the cluster yielded a negative value for the real part of γ, Reγ = − 4.8 × 10−29 esu. These numerical values are in good agreement with those obtained in a Z-scan experiment. Even though the clusters absorb laser light at 532 nm significantly, the results of temporal profile analysis on transmitted pulses show that the solvent thermal effect makes little contribution to the observed nonlinear optical phenomenon.

The sacrificial thermal shutter/reflector concept is suitable for optical power limiting in optical systems containing an intermediate focus and uses a thermally activated chemical process to form a mirror that reflects a large fraction of the incident laser light. Under normal illumination, the thermal reflector component is a transmissive optical element at or near a focal plane of an optical system. A pulse from an incident laser beam heats a film of precursor chemicals on the optical element and thereby converts it to a localized reflective metallic mirror. For visible laser pulses longer than 0.1 ms, the thermal shutter provides optical limiting at energies below the ANSI Maximum Permissible Exposure (MPE) standard for laser eye protection. For shorter pulses, near-MPE limiting is achieved. See-through during exposure is also possible with these elements. Various thermal shutter chemistries and efforts to form optically clear thin precursor films are described. The laser testing results highlight the importance of the substrate and absorber in these devices.

Using micro-capillaries and capillary arrays, we have fabricated dye- and C60-doped liquid crystal cored fibers and image transmission plates of various core diameters and lengths. We have observed nonlinear pulse propagation and limiting effect using nanosecond 0.53 μm Nd:Yag laser. Typical threshold fluence is on the order of < 1 J/cm2 in a 7 mm long fiber. A theoretical modelling of the observed effect is also presented.

Application of highly polar dative bonds of heteroatoms to boron atoms for the preparation of a new class of liquid crystals is discussed. Semiempirical calculations show that compounds incorporating polar bonds of tetra- and higher-coordinated boron centers are characterized by large coaxial dipole moments and relatively large first hyperpolarizabilities β. It is expected that these new liquid crystalline materials will be useful for electrooptical applications.